A wireless device (e.g., a cellular phone or a smartphone) in a wireless communication system may include a radio frequency (RF) transceiver to transmit and receive data for two-way communication. A mobile RF transceiver may include a transmit section for data transmission and a receive section for data reception of a communication signal. For data transmission, the transmit section may modulate an RF carrier signal with data to obtain a modulated RF signal, amplify the modulated RF signal to obtain an amplified RF signal having the proper output power level, and transmit the amplified RF signal via an antenna to a base station. For data reception, the receive section may obtain a received RF signal via the antenna. The receive section may amplify and process the received RF signal to recover data sent by a base station in a communication signal.
A mobile RF transceiver may include one or more circuits for amplifying these communication signals. The amplifier circuits may include one or more amplifier stages that may have one or more driver stages and one or more amplifier output stages. Each of the amplifier stages includes one or more transistors configured in various ways to amplify the communication signals. Various options exist for fabricating the transistors that are configured to amplify the communication signals transmitted and received by mobile RF transceivers.
The design of these mobile RF transceivers may include the use of semiconductor on insulator (SOI) technology for transistor fabrication. SOI technology replaces conventional semiconductor substrates with a layered semiconductor-insulator-semiconductor substrate to reduce parasitic capacitance and improve performance. SOI-based devices differ from conventional, silicon-built devices because a silicon junction is above an electrical isolator, typically a buried oxide (BOX) layer. A reduced thickness of the BOX layer, however, may not sufficiently reduce the parasitic capacitance caused by the proximity of an active device on the semiconductor layer and a semiconductor substrate supporting the BOX layer.
The active devices on the SOI layer may include complementary metal oxide semiconductor (CMOS) transistors. Unfortunately, successful fabrication of transistors using SOI technology is complicated by parasitic capacitance. For example, parasitic capacitance in the form of contact/interconnect-to-gate capacitance is caused by proximity of back-end-of-line (BEOL) interconnects and/or middle-of-line (MOL) contacts and the transistor gates. This additional capacitance causes adverse effects, such as circuit delays and losses. This additional capacitance is especially problematic for low noise amplifiers (LNAs), which may prevent support for 5G applications.